Begining sometime this afternoon, LionMail users may have noticed delays in delivery of messages that contain attachments or are very large in size. Google investigated this issue and believes it is resolved, though it is possible delayed mail has not yet arrived; it is expected shortly. According to their status page, this was resolved by 4:52pm EST.
Google status can be seen here, as an orange dot for Mail on 1/23/13:
and today's outage is described here:
Like Google, we apologize for the inconvenience and thank you for your patience and continued support.
For a complete list of recent and upcoming scheduled service changes, please visit http://www.columbia.edu/acis/alerts-list.html.